Method of treating a subterranean hydrocarbon-bearing formation

ABSTRACT

Improved treatment of a subterranean hydrocarbon-bearing formation is effected by fracturing the formation using a fracturing mixture composed of a hydrocarbon liquid containing, in addition to a particulate propping agent, finely suspended charcoal, whereby additional fracturing is attained after a conventional fracturing procedure by in situ combustion of the fracturing mixture, and thereafter quenching the combustion with water.

Unite tates ate [is] 3,638,727

Allen et a1. Feb. 1, 1972 [54] METHOD OF TREATING A 3,010,513 11/1961Gerner ..l66/259 3,366,176 1/1968 Parrish ..166/259 SUBTERRANEANHYDRQCARBON' 3,376,929 4/1968 Hagedom ..166/260 x BEARING FORMATIONPrimary Examiner-Stephen J. Novosad [72] hwemm' $35: fix fg g ifAtt0rneyK. E. Kavanagh and Thomas H. Whale-y V V w [73] Assignee: TexacoInc., New York, N.Y.

[22] Filed: Sept. 27, 1968 57 ABSTRACT 21 Appl.No.: 786,791 1 Improvedtreatment of a subterranean hydrocarbon-bearing formation is effected byfracturing the formation using a frac- [52] US. Cl ..166/259, 166/260,166/261, turing mixture composed of a hydrocarbon liquid containing,166/262 in addition to a particulate propping agent, finely suspended[51] Int. Cl .3221! 43/24 charcoal, whereby addifimlal fracturing isattained after a [58] Field of Search 166/259 256 260 261 262463ventional fracturing procedure by in situ combustion of the I 6g/308fracturing mixture, and thereafter quenching the combustion with water.

[561 R i 'f i lf t wi M, U

UNITED STATES PATENTS 2,962,095 11/1960 Me g [g 9 A 4 Claims, NoDrawings METHOD OF TREATING A SUBTERRANEAN HYDROCARBON-BEARING FORMATIONFIELD OF THE lNVENTlON This invention relates to an improved method fortreatment of a subterranean hydrocarbon-bearing formation leading toincreased recovery of hydrocarbons therefrom. More particularly, thisinvention relates to a method whereby stimulation of a subterraneanhydrocarbon-bearing formation is realized by subjecting the formation toa conventional hydraulic fracturing operation, effecting in situcombustion of the fracturing mixture, and thereafter quenching thecombustion with water.

DESCRIPTION OF THE PRIOR ART In the production of hydrocarbons fromsubterranean for mations, one of the methods used to stimulateproduction is that of fracturing the subterranean formation wherebyartificial fractures or cleavage planes are formed extending from thewell bore into the hydrocarbon-bearing formation. These cleavage planesincrease the permeability and porosity of the formation and thus provideflow channels which enhance the production of hydrocarbons.

The most commonly used procedure to induce fracturing is high-pressurehydraulic fracturing. In that process, a fluid is displaced down a wellbore and into contact with the hydrocarbon-bearing formation at a ratehigher than that at which the fluid can flow into and through theformation. On continued injection of the fluid, the pressure within thewell bore increases to a pressure at which the formation breaks down tocreate one or more fractures extending outwardly from the well bore intothe formation. Hydraulic fracturing fluids generally consist of aqueousliquids, hydrocarbon oils, or oil-water emulsions, to which proppingagents, viscosity thickeners, or other additives have been added.

Usually, after the artificial fractures have been created around a wellbore within a hydrocarbon-bearing formation, the solid particulatepropping agents are caused to flow into the fracture and function tohold the fracture at least partially open after release of fracturingpressure on the fluid in the well bore and in the fracture and therebyprovide a highcapacity flow conduit to improve the fluid conductivitiesof the formation. While sand is the usual propping agent used formaintaining passages or channels within the fracture leading to the wellbore, other particulate materials such as metal shot, glass beads, andplastics, which have a high compressive strength, are used also.

Another technological advance in the petroleum industry is thedevelopment of secondary recovery methods to increase the ultimaterecovery of hydrocarbons from subterranean formations. Among the newertechniques used are thermal methods, including in situ combustion.Briefly, this method involves initiating a combustion of part of thehydrocarbons in the formation and thereafter maintaining the in situcombustion by the continuous injection of a combustion-supporting gas,such as air, which burns pat of the hydrocarbons, thereby providingthermal energy for the displacement of the remainder of the hydrocarbonstoward a production well, whence it is produced.

in accordance with the present invention, it is an object thereof toprovide an improved method for treatment of a subterraneanhydrocarbon-bearing formation to enhance or otherwise improve therecovery of hydrocarbons therefrom.

It is another object to provide a method for stimulating hydrocarbonproduction of a subterranean hydrocarbon-bearing formation by increasingthe porosity and permeability of the formation by the in situ combustionof a fracturing mixture, whereby a much greater improvement in terms ofincremental barrels per day of hydrocarbons produced can be realized.

It is a further object to utilize an in situ combustion whereby theattendant thermal effects induce increased fracturing of thehydrocarbon-bearing formation over that attained by conventionalfracturing methods.

SUMMARY This invention relates to a secondary recovery operation bysubjecting a subterranean hydrocarbon-bearing formation, which hasundergone a hydraulic fracturing operation, to an in situ combustion ofthe hydraulic fracturing mixture in the additional channels so formed,and thereafter injecting water into the formation to induce furtheradditional fractures by thermal shock.

DESCRIPTlON OF THE METHOD More specifically, it has been found that intests involving the development of ignition systems for the initiationof in situ combustion, temperatures in excess of 2,000 F. have beenattained in the formation adjacent a well bore by the use of acombustion hydrocarbon such as kerosene containing charcoal.Furthermore, subsequent examination of the formation matrix has shownthat the accompanying high temperatures have resulted in the formationbeing irreversibly altered as manifested by increases in itspermeability and porosity.

In the application of this invention, there is introduced into asubterranean formation, via a well penetrating the formation, afracturing mixture consisting of a combustible hydrocarbon fluid such askerosene, a particulate propping agent such as sand, and finelydispersed charcoal. After a conventional fracturing operation has beenconducted by wellknown techniques to the point where fracturing hasoccurred as indicated by a pressure decline and the mixture has beendisplaced into the formation, the mixture is ignited within theformation immediately adjacent the well bore by any techniques known inthe art, such as electrical heating devices or chemical methods.However, the preferred igniter is an incendiary device, such as acharcoal package saturated with kerosene, which would be positionedacross the hydrocarbonbearing formation and then ignited usinginitiators such as electrical squibs or chemical fuses, during whichtime air would be injected in the well bore.

After ignition had been initiated, air \vould continue to be injected tomaintain the combustion, and to continue the combustion of the hydraulicfracturing mixture. After in situ combustion of the hydraulic mixturehad been completed, injection of the air would be terminated, and anaqueous medium, such as water or brine, would be introduced into theformation via the well bore to subject the hot zone swept by the in situcombustion to thermal shock thereby leading to additional fracturing ofthe formation.

While we do not wish to be bound by any particular theory, it ispostulated that as a result of the in situ combustion, the physicalcharacteristics of the formation swept by the high temperature willexhibit improved porosity and permeability. lt is believe also that thehigh temperature will cause clays subjected thereto to lose water andbecome otherwise irreversibly dehydrated with resultant volumeshrinkage. It is believed also that thermal fracturing of the formationswept or otherwise influence by the high temperature will occur by shearexpansion along formation discontinuities. Further, it is believed thatat the high temperature generated by the in situ combustion will effectcalcination or thermal decomposition of many of the minerals present,such as limestone or dolomite, which were exposed to these hightemperatures.

Illustrative of this invention, a mixture containing 50,000 pounds ofsand and 50,000 pounds of charcoal admixed with 3,500 barrels ofkerosene is used for fracturing. A conventional hydraulic fracturingoperation is conducted whereby formation fractures are induced in thevicinity of the well bore. Ignition of the fracturing mixture is thenaccomplished by use of an incendiary charge positioned across thehydrocarhon-bearing formation. Air is injected continuously to continuethe combustion of the fracturing mixture, thereby generating about20,000 MMB.t.u. For an estimated air requirement of MMc.f.,approximately 30 to 40 days would be required for the in situ combustionoperation. Following combustion of the fracturing mixture, water orbrine is injected to quench the combustion, rapidly cool the heatedformation, and thereby induce additional fracturing of the formation bythermal shock. Thereafter, the well would be produced to recoveradditional hydrocarbons.

It will be apparent from the foregoing description that the method issubject to other modifications without departing from the scope of theinvention as defined in the following claims.

We claim:

1. in a method of treating a subterranean hydrocarbonbearing formationpenetrated by a well bore via which a combustible hydraulic fracturingmixture has been injected into said formation with resultant hydraulicfracturing thereof, the improvement comprising the steps of a.introducing via said well bore a combustion-supporting gas into thatportion of said formation containing said hydraulic fracturing mixture,

b. initiating in situ combustion of said hydraulic fracturing mixturewithin said formation,

0. continuing combustion of said hydraulic fracturing mixture untiltemperatures in excess of 2,000 F. have been attained in the formationadjacent the well bore,

d. discontinuing introducing said combustion-supporting gas into saidformation to terminate said in situ combustion process,

e. introducing via said well bore an aqueous media into that portion ofsaid formation wherein said in situ combustion has occurred to effect athermal quench of said formation with resultant additional fracturing ofsaid formation by thermal shock and thereafter,

f. producing said hydrocarbon via said well bore from said formation.

2. The method as defined in claim 1 wherein said combustible hydraulicfracturing mixture consists of a liquid petroleum fraction containingtherein a particulate propping agent, comprising in admixture therewithfinely suspended charcoal.

3. The method of claim 2 wherein said aqueous media is water, brine andmixtures thereof.

4. The method of claim 3 wherein said combustion-supporting gas is air.

2. The method as defined in claim 1 wherein said combustible hydraulicfracturing mixture consists of a liquid petroleum fraction containingtherein a particulate propping agent, comprising in admixture therewithfinely suspended charcoal.
 3. The method of claim 2 wherein said aqueousmedia is water, brine and mixtures thereof.
 4. The method of claim 3wherein said combustion-supporting gas is air.